Unitary electromechanical filter vibrator having individual resonant elements coupled together by mechanically strong and electrically weak bridges



A nl 5, 1966 F. J. SCHOFER 3,2 2

UNITARY ELECTROMECHANICAL FILTER VIBRATOR HAVING INDIVIDUAL RESONANT ELEMENTS COUPLED TOGETHER BY MECHANIGALLY STRONG AND ELECTHICALLY WEAK BRIDGES Filed Jan. 31, 1963 Fig.1

(PRIOR ART) United States Patent 2 Claims. (a. 333-72 The invention disclosed herein is concerned with an electromechanical filter of the type disclosed in the copending application Serial No. 817,355, filed June 1, 1959, now Patent No. 3,086,183, which is owned by the assignee named in the present case, comprising at least two plateor strip-shaped mechanical resonators which are connected by means of mechanical coupling webs to form a mechanically compact unit.

The various objects and features of the invention will appear from the description which is rendered below with reference to the accompanying drawing.

FIG. 1 shows an example of an electromechanical filter constructed according to the above noted prior application;

FIG. 2 illustrates an electromechanical filter according to the present invention; and

FIG. 3 indicates an example of an electromechanical filter comprising two rod-shaped resonators.

Electromechanical filters constructed according to the prior application are usually made of a rectangularly shaped quartz plate which is by appropriate cutouts subdivided to form individual resonators and coupling members for connecting such resonators. An example of such a filter is shown in FIG. 1. The filter comprises two planar shear resonators which are connected by way of a small coupling bridge having a length l, a width b, and a thickness corresponding substantially to that of the square resonators. The entire filter consists of a thin quartz plate which is provided with cutouts so as to form the two resonators. However, the coupling factor between the two resonators is with this configuration limited toward low coupling values. It must be considered in this connection that the mechanical stability becomes progressively lower in the sense of reducing the coupling factor, upon enlarging l and reducing b.

The object underlying the invention is to reduce the dufiiculties insofar as a sufficient mechanical stability of the entire filter is concerned, which are with small coupling factors experienced with an electromechanical filter wherein the individual resonators are interconnected by coupling bridges.

This object is achieved in connection with an electromechanical filter comprising at least two plateor stripshaped (i.e. planar) mechanical resonators which are by means of mechanical coupling webs or bridges connected to form a mechanically compact unit, by making the central region of the individual coupling web of greater crosssectional area than at the ends thereof which border on the respective resonators.

The entire filter body consists advantageously of a plate which is subdivided by cutouts provided therein, to form resonators and the coupling webs.

It is moreover advantageous to form the respective coupling web so that it has in its central region, excepting the dimensions which are decisive for its individual resonance, which are appropriate for the oscillation mode of the resonators, at least nearly the same dimensions as the resonators, and to make the dimension which is decisive for its individual resonance different as compared with the dimensions of the resonators, so that the individual resonance of the coupling web is far removed from the individual resonance of the resonators. The structure according to the invention was found to be particularly suitable in connection with resonators operating with a planar shear oscillation.

The embodiment of an electromechanical filter according to the invention, as shown in FIG, 2, comprises two mechanical resonators 1, 2, formed as planar shear oscillators, and a coupling element 3. The entire filter consists of a quartz plate which is by cutouts 4 subdivided to form the resonators and the coupling member. The coupling member is of considerable length l and its central region or part is appreciably wider than the ends thereof which merge with the respective resonators 1 and 2, such end portions having a width b.

The novel configuration of the oscillating body, in which are formed two cutouts, spaced apart by a given amount, makes it possible to extend the region of the coupling factor between the resonators 1 and 2, toward lower values, up to less than 1%0. It is, however, important that the intermediate member 3, which is in the corresponding embodiment of the same width as the resonators 1 and 2, is of a length, as seen in axial direction of the filter, which is so much shorter than the length of the resonators proper, that the individual resonance thereof is appreciably higher than the individual resonance of the resonators 1 and 2.

While the embodiment according to FIG. 2 comprises as resonators square planar shear oscillators, the invention is likewise applicable in connection with resonators operating as longitudinal oscillators or as bending oscillators, it being in such cases merely important that the coupling is effected by way of intermediate members having an individual resonance which is appreciably different from the individual resonance of the resonators proper.

The configuration of the coupling member according to the invention, can also be applied in the case of rods which are interconnected by means of coupling webs or bridges. An example of such structure is shown in FIG. 3, showing a filter made of two rod-shaped resonators 5 and 6 which are connected by means of a coupling bridge 7. The resonators 5, 6 and the coupling member 7 are here again formed by cutouts 4 provided in the unitary filter body.

The planar shear oscillation was found particularly advantageous as an oscillation mode for a filter of the last noted type. The provision of a small coupling factor, particularly in connection with rods executing planar shear oscillations, is indeed made possible only in this manner, since the rods become in higher frequency positions very narrow, making it possible to provide only shallow cutouts so as to avoid jeopardizing the mechanical stability of the oscillating body.

The designation elongated planar body or member is intended to encompass plate-shaped and strip-shaped and also rod-like elements.

Changes may be made Within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. An electromechanical filter comprising at least two elongated planar elements forming resonators which are connected over mechanical coupling bridges into a unitary structure, such individual coupling bridge being subdivided into three regions, the central region of which has a larger cross-sectional area than the adjacent regions bordering the resonators connected thereby, the length of the central region, in the direction of the longitudinal axis of the filter, being considerably greater than the corresponding length of said bordering regions, the dimensions of the individual central region, determinative for its own resonance corresponding to the oscillation type of the resonators, being so selected with respect to the corresponding dimensions of the resonators that the individual resonance of the coupling bridge is far removed from the individual resonance of the respective resonators.

2. A filter according to claim 1, wherein the entire filter body comprises a plate-like element subdivided by relatively narrow notches to form the resonators and coupling bridges, each individual coupling bridge having in its central region, excepting the dimensions which are decisive for its individual resonance, appropriatev for the oscillation mode of the resonators, at least nearly the same dimensions as the resonators, the individual resonators being constructed so as to operate as planar shear oscillators.

References Cited bythe Examiner UNITED STATES PATENTS Bohannon 333-72 Roberts 3,33-71 Honda '333.72 Mason 333F71 Schofer 333-.72

HERMAN KARL SAALBACH, Primary Examiner. ELI LIEBERMAN, Examiner. 

1. AN ELECTROMECHANICAL FILTER COMPRISING AT LEAST TWO ELONGATED PLANAR ELEMENTS FORMING RESONATORS WHICH ARE CONNECTED OVER MECHANICAL COUPLING BRIDGES INTO A UNITARY STRUCTURE, SUCH INDIVIDUAL COUPLING BRIDGE BEING SUBDIVIDED INTO THREE REGIONS, THE CENTRAL REGION OF WHICH HAS A LARGER CROSS-SECTIONAL AREA THAN THE ADJACENT REGIONS BORDERING THE RESONATORS CONNECTED THEREBY, THE LENGTH OF THE CENTRAL REGION, IN THE DIRECTION OF THE LONGITUDINAL AXIS OF THE FILTER, BEING CONSIDERABLY GREATER THAN THE CORRESPONSING LENGTH OF SAID BORDERING REGIONS, THE DIMENSIONS OF THE INDIVIDUAL CENTRAL REGION, DETERMINATIVE FOR ITS OWN RESONANCE CORRESPONDING TO THE OSCILLATION TYPE OF THE RESONATORS, BEING SO SELECTED WITH RESPECT TO THE CORRESPONDING DIMENSIONS OF THE RESONATORS THAT THE INDIVIDUAL RESONANCE OF THE COUPLING BRIDGE IS FAR REMOVED FROM THE INDIVIDUAL RESONANCE OF THE RESPECTIVE RESONATORS. 